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 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.util;

/**
 * A {@link NavigableSet} implementation based on a {@link TreeMap}.
 * The elements are ordered using their {@linkplain Comparable natural
 * ordering}, or by a {@link Comparator} provided at set creation
 * time, depending on which constructor is used.
 *
 * <p>This implementation provides guaranteed log(n) time cost for the basic
 * operations ({@code add}, {@code remove} and {@code contains}).
 *
 * <p>Note that the ordering maintained by a set (whether or not an explicit
 * comparator is provided) must be <i>consistent with equals</i> if it is to
 * correctly implement the {@code Set} interface.  (See {@code Comparable}
 * or {@code Comparator} for a precise definition of <i>consistent with
 * equals</i>.)  This is so because the {@code Set} interface is defined in
 * terms of the {@code equals} operation, but a {@code TreeSet} instance
 * performs all element comparisons using its {@code compareTo} (or
 * {@code compare}) method, so two elements that are deemed equal by this method
 * are, from the standpoint of the set, equal.  The behavior of a set
 * <i>is</i> well-defined even if its ordering is inconsistent with equals; it
 * just fails to obey the general contract of the {@code Set} interface.
 *
 * <p><strong>Note that this implementation is not synchronized.</strong>
 * If multiple threads access a tree set concurrently, and at least one
 * of the threads modifies the set, it <i>must</i> be synchronized
 * externally.  This is typically accomplished by synchronizing on some
 * object that naturally encapsulates the set.
 * If no such object exists, the set should be "wrapped" using the
 * {@link Collections#synchronizedSortedSet Collections.synchronizedSortedSet}
 * method.  This is best done at creation time, to prevent accidental
 * unsynchronized access to the set: <pre>
 *   SortedSet s = Collections.synchronizedSortedSet(new TreeSet(...));</pre>
 *
 * <p>The iterators returned by this class's {@code iterator} method are
 * <i>fail-fast</i>: if the set is modified at any time after the iterator is
 * created, in any way except through the iterator's own {@code remove}
 * method, the iterator will throw a {@link ConcurrentModificationException}.
 * Thus, in the face of concurrent modification, the iterator fails quickly
 * and cleanly, rather than risking arbitrary, non-deterministic behavior at
 * an undetermined time in the future.
 *
 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
 * as it is, generally speaking, impossible to make any hard guarantees in the
 * presence of unsynchronized concurrent modification.  Fail-fast iterators
 * throw {@code ConcurrentModificationException} on a best-effort basis.
 * Therefore, it would be wrong to write a program that depended on this
 * exception for its correctness:   <i>the fail-fast behavior of iterators
 * should be used only to detect bugs.</i>
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @param <E> the type of elements maintained by this set
 * @author Josh Bloch
 * @see Collection
 * @see Set
 * @see HashSet
 * @see Comparable
 * @see Comparator
 * @see TreeMap
 * @since 1.2
 */

public class TreeSet<E> extends AbstractSet<E>
    implements NavigableSet<E>, Cloneable, java.io.Serializable {

  /**
   * The backing map.
   */
  private transient NavigableMap<E, Object> m;

  // Dummy value to associate with an Object in the backing Map
  private static final Object PRESENT = new Object();

  /**
   * Constructs a set backed by the specified navigable map.
   */
  TreeSet(NavigableMap<E, Object> m) {
    this.m = m;
  }

  /**
   * Constructs a new, empty tree set, sorted according to the
   * natural ordering of its elements.  All elements inserted into
   * the set must implement the {@link Comparable} interface.
   * Furthermore, all such elements must be <i>mutually
   * comparable</i>: {@code e1.compareTo(e2)} must not throw a
   * {@code ClassCastException} for any elements {@code e1} and
   * {@code e2} in the set.  If the user attempts to add an element
   * to the set that violates this constraint (for example, the user
   * attempts to add a string element to a set whose elements are
   * integers), the {@code add} call will throw a
   * {@code ClassCastException}.
   */
  public TreeSet() {
    this(new TreeMap<E, Object>());
  }

  /**
   * Constructs a new, empty tree set, sorted according to the specified
   * comparator.  All elements inserted into the set must be <i>mutually
   * comparable</i> by the specified comparator: {@code comparator.compare(e1,
   * e2)} must not throw a {@code ClassCastException} for any elements
   * {@code e1} and {@code e2} in the set.  If the user attempts to add
   * an element to the set that violates this constraint, the
   * {@code add} call will throw a {@code ClassCastException}.
   *
   * @param comparator the comparator that will be used to order this set. If {@code null}, the
   * {@linkplain Comparable natural ordering} of the elements will be used.
   */
  public TreeSet(Comparator<? super E> comparator) {
    this(new TreeMap<>(comparator));
  }

  /**
   * Constructs a new tree set containing the elements in the specified
   * collection, sorted according to the <i>natural ordering</i> of its
   * elements.  All elements inserted into the set must implement the
   * {@link Comparable} interface.  Furthermore, all such elements must be
   * <i>mutually comparable</i>: {@code e1.compareTo(e2)} must not throw a
   * {@code ClassCastException} for any elements {@code e1} and
   * {@code e2} in the set.
   *
   * @param c collection whose elements will comprise the new set
   * @throws ClassCastException if the elements in {@code c} are not {@link Comparable}, or are not
   * mutually comparable
   * @throws NullPointerException if the specified collection is null
   */
  public TreeSet(Collection<? extends E> c) {
    this();
    addAll(c);
  }

  /**
   * Constructs a new tree set containing the same elements and
   * using the same ordering as the specified sorted set.
   *
   * @param s sorted set whose elements will comprise the new set
   * @throws NullPointerException if the specified sorted set is null
   */
  public TreeSet(SortedSet<E> s) {
    this(s.comparator());
    addAll(s);
  }

  /**
   * Returns an iterator over the elements in this set in ascending order.
   *
   * @return an iterator over the elements in this set in ascending order
   */
  public Iterator<E> iterator() {
    return m.navigableKeySet().iterator();
  }

  /**
   * Returns an iterator over the elements in this set in descending order.
   *
   * @return an iterator over the elements in this set in descending order
   * @since 1.6
   */
  public Iterator<E> descendingIterator() {
    return m.descendingKeySet().iterator();
  }

  /**
   * @since 1.6
   */
  public NavigableSet<E> descendingSet() {
    return new TreeSet<>(m.descendingMap());
  }

  /**
   * Returns the number of elements in this set (its cardinality).
   *
   * @return the number of elements in this set (its cardinality)
   */
  public int size() {
    return m.size();
  }

  /**
   * Returns {@code true} if this set contains no elements.
   *
   * @return {@code true} if this set contains no elements
   */
  public boolean isEmpty() {
    return m.isEmpty();
  }

  /**
   * Returns {@code true} if this set contains the specified element.
   * More formally, returns {@code true} if and only if this set
   * contains an element {@code e} such that
   * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
   *
   * @param o object to be checked for containment in this set
   * @return {@code true} if this set contains the specified element
   * @throws ClassCastException if the specified object cannot be compared with the elements
   * currently in the set
   * @throws NullPointerException if the specified element is null and this set uses natural
   * ordering, or its comparator does not permit null elements
   */
  public boolean contains(Object o) {
    return m.containsKey(o);
  }

  /**
   * Adds the specified element to this set if it is not already present.
   * More formally, adds the specified element {@code e} to this set if
   * the set contains no element {@code e2} such that
   * <tt>(e==null&nbsp;?&nbsp;e2==null&nbsp;:&nbsp;e.equals(e2))</tt>.
   * If this set already contains the element, the call leaves the set
   * unchanged and returns {@code false}.
   *
   * @param e element to be added to this set
   * @return {@code true} if this set did not already contain the specified element
   * @throws ClassCastException if the specified object cannot be compared with the elements
   * currently in this set
   * @throws NullPointerException if the specified element is null and this set uses natural
   * ordering, or its comparator does not permit null elements
   */
  public boolean add(E e) {
    return m.put(e, PRESENT) == null;
  }

  /**
   * Removes the specified element from this set if it is present.
   * More formally, removes an element {@code e} such that
   * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>,
   * if this set contains such an element.  Returns {@code true} if
   * this set contained the element (or equivalently, if this set
   * changed as a result of the call).  (This set will not contain the
   * element once the call returns.)
   *
   * @param o object to be removed from this set, if present
   * @return {@code true} if this set contained the specified element
   * @throws ClassCastException if the specified object cannot be compared with the elements
   * currently in this set
   * @throws NullPointerException if the specified element is null and this set uses natural
   * ordering, or its comparator does not permit null elements
   */
  public boolean remove(Object o) {
    return m.remove(o) == PRESENT;
  }

  /**
   * Removes all of the elements from this set.
   * The set will be empty after this call returns.
   */
  public void clear() {
    m.clear();
  }

  /**
   * Adds all of the elements in the specified collection to this set.
   *
   * @param c collection containing elements to be added to this set
   * @return {@code true} if this set changed as a result of the call
   * @throws ClassCastException if the elements provided cannot be compared with the elements
   * currently in the set
   * @throws NullPointerException if the specified collection is null or if any element is null and
   * this set uses natural ordering, or its comparator does not permit null elements
   */
  public boolean addAll(Collection<? extends E> c) {
    // Use linear-time version if applicable
    if (m.size() == 0 && c.size() > 0 &&
        c instanceof SortedSet &&
        m instanceof TreeMap) {
      SortedSet<? extends E> set = (SortedSet<? extends E>) c;
      TreeMap<E, Object> map = (TreeMap<E, Object>) m;
      Comparator<?> cc = set.comparator();
      Comparator<? super E> mc = map.comparator();
      if (cc == mc || (cc != null && cc.equals(mc))) {
        map.addAllForTreeSet(set, PRESENT);
        return true;
      }
    }
    return super.addAll(c);
  }

  /**
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException if {@code fromElement} or {@code toElement} is null and this set
   * uses natural ordering, or its comparator does not permit null elements
   * @throws IllegalArgumentException {@inheritDoc}
   * @since 1.6
   */
  public NavigableSet<E> subSet(E fromElement, boolean fromInclusive,
      E toElement, boolean toInclusive) {
    return new TreeSet<>(m.subMap(fromElement, fromInclusive,
        toElement, toInclusive));
  }

  /**
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException if {@code toElement} is null and this set uses natural ordering,
   * or its comparator does not permit null elements
   * @throws IllegalArgumentException {@inheritDoc}
   * @since 1.6
   */
  public NavigableSet<E> headSet(E toElement, boolean inclusive) {
    return new TreeSet<>(m.headMap(toElement, inclusive));
  }

  /**
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException if {@code fromElement} is null and this set uses natural ordering,
   * or its comparator does not permit null elements
   * @throws IllegalArgumentException {@inheritDoc}
   * @since 1.6
   */
  public NavigableSet<E> tailSet(E fromElement, boolean inclusive) {
    return new TreeSet<>(m.tailMap(fromElement, inclusive));
  }

  /**
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException if {@code fromElement} or {@code toElement} is null and this set
   * uses natural ordering, or its comparator does not permit null elements
   * @throws IllegalArgumentException {@inheritDoc}
   */
  public SortedSet<E> subSet(E fromElement, E toElement) {
    return subSet(fromElement, true, toElement, false);
  }

  /**
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException if {@code toElement} is null and this set uses natural ordering,
   * or its comparator does not permit null elements
   * @throws IllegalArgumentException {@inheritDoc}
   */
  public SortedSet<E> headSet(E toElement) {
    return headSet(toElement, false);
  }

  /**
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException if {@code fromElement} is null and this set uses natural ordering,
   * or its comparator does not permit null elements
   * @throws IllegalArgumentException {@inheritDoc}
   */
  public SortedSet<E> tailSet(E fromElement) {
    return tailSet(fromElement, true);
  }

  public Comparator<? super E> comparator() {
    return m.comparator();
  }

  /**
   * @throws NoSuchElementException {@inheritDoc}
   */
  public E first() {
    return m.firstKey();
  }

  /**
   * @throws NoSuchElementException {@inheritDoc}
   */
  public E last() {
    return m.lastKey();
  }

  // NavigableSet API methods

  /**
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException if the specified element is null and this set uses natural
   * ordering, or its comparator does not permit null elements
   * @since 1.6
   */
  public E lower(E e) {
    return m.lowerKey(e);
  }

  /**
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException if the specified element is null and this set uses natural
   * ordering, or its comparator does not permit null elements
   * @since 1.6
   */
  public E floor(E e) {
    return m.floorKey(e);
  }

  /**
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException if the specified element is null and this set uses natural
   * ordering, or its comparator does not permit null elements
   * @since 1.6
   */
  public E ceiling(E e) {
    return m.ceilingKey(e);
  }

  /**
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException if the specified element is null and this set uses natural
   * ordering, or its comparator does not permit null elements
   * @since 1.6
   */
  public E higher(E e) {
    return m.higherKey(e);
  }

  /**
   * @since 1.6
   */
  public E pollFirst() {
    Map.Entry<E, ?> e = m.pollFirstEntry();
    return (e == null) ? null : e.getKey();
  }

  /**
   * @since 1.6
   */
  public E pollLast() {
    Map.Entry<E, ?> e = m.pollLastEntry();
    return (e == null) ? null : e.getKey();
  }

  /**
   * Returns a shallow copy of this {@code TreeSet} instance. (The elements
   * themselves are not cloned.)
   *
   * @return a shallow copy of this set
   */
  @SuppressWarnings("unchecked")
  public Object clone() {
    TreeSet<E> clone;
    try {
      clone = (TreeSet<E>) super.clone();
    } catch (CloneNotSupportedException e) {
      throw new InternalError(e);
    }

    clone.m = new TreeMap<>(m);
    return clone;
  }

  /**
   * Save the state of the {@code TreeSet} instance to a stream (that is,
   * serialize it).
   *
   * @serialData Emits the comparator used to order this set, or {@code null} if it obeys its
   * elements' natural ordering (Object), followed by the size of the set (the number of elements it
   * contains) (int), followed by all of its elements (each an Object) in order (as determined by
   * the set's Comparator, or by the elements' natural ordering if the set has no Comparator).
   */
  private void writeObject(java.io.ObjectOutputStream s)
      throws java.io.IOException {
    // Write out any hidden stuff
    s.defaultWriteObject();

    // Write out Comparator
    s.writeObject(m.comparator());

    // Write out size
    s.writeInt(m.size());

    // Write out all elements in the proper order.
    for (E e : m.keySet()) {
      s.writeObject(e);
    }
  }

  /**
   * Reconstitute the {@code TreeSet} instance from a stream (that is,
   * deserialize it).
   */
  private void readObject(java.io.ObjectInputStream s)
      throws java.io.IOException, ClassNotFoundException {
    // Read in any hidden stuff
    s.defaultReadObject();

    // Read in Comparator
    @SuppressWarnings("unchecked")
    Comparator<? super E> c = (Comparator<? super E>) s.readObject();

    // Create backing TreeMap
    TreeMap<E, Object> tm = new TreeMap<>(c);
    m = tm;

    // Read in size
    int size = s.readInt();

    tm.readTreeSet(size, s, PRESENT);
  }

  /**
   * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
   * and <em>fail-fast</em> {@link Spliterator} over the elements in this
   * set.
   *
   * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
   * {@link Spliterator#DISTINCT}, {@link Spliterator#SORTED}, and
   * {@link Spliterator#ORDERED}.  Overriding implementations should document
   * the reporting of additional characteristic values.
   *
   * <p>The spliterator's comparator (see
   * {@link java.util.Spliterator#getComparator()}) is {@code null} if
   * the tree set's comparator (see {@link #comparator()}) is {@code null}.
   * Otherwise, the spliterator's comparator is the same as or imposes the
   * same total ordering as the tree set's comparator.
   *
   * @return a {@code Spliterator} over the elements in this set
   * @since 1.8
   */
  public Spliterator<E> spliterator() {
    return TreeMap.keySpliteratorFor(m);
  }

  private static final long serialVersionUID = -2479143000061671589L;
}
